1. Field of the Invention
The present invention relates to apparatus for forming multicolor images in accordance with image data read by image reading means including a photoelectric transducer, and more particularly to a color image forming apparatus, for example, for use as an electronic print board which has a writing surface like a white board for writing a multicolor image thereon with pen means and which comprises reading means for reading the image and printing means for printing a multicolor image in accordance with the read image data.
2. Description of the Related Art
Recently electronic print boards have been introduced into use, for example, in meetings which are adapted to print on paper images written on a white board or sheet with a felt pen or the like. With these electronic print boards, the image written on the writing surface is read optically, and the resulting image data is printed out by a thermal printer or the like.
Writing implements of more than one color, as of black, red and blue, are usable for electronic print boards, whereas the print boards presently in use are adapted to produce monochromatic (usually black) prints only and are unable to reproduce the written image in different colors as intended by the writer.
On the other hand, the conventional image forming apparatus of digital color copying machines or the like are adapted to read the image of the original through three color separation filters, for example, of red, green and blue to obtain image data as separated in the three colors, and thereafter reproduce a color image according to the image data by the combination of three primary colors, i.e., cyan, yellow and magenta, or of four colors further including black.
Since the colors of writing implements actually in use for electronic print boards are primarily the three colors of black, red and blue, the image to be thereby reproduced need not have as many colors as those produced by usual color printers, nor is it always necessary to reproduce the colors of writing implements with high fidelity. Accordingly, the direct application of conventional color printing techniques to the production of color prints by electronic print boards is not justifiable in respect of control and construction and is also economically disadvantageous.
Further because colors other than black, red blue are seldom used for common documents, the image forming apparatus for copying machines are similarly unjustifiable in respect of control and construction when there is no particular need to use such other colors.
It is presently thought most advantageous from the viewpoint of cost and compacting the printing unit to use the thermal transfer system for color printing. With this system, however, it is required to superimpose three colors for the reproduction of black and two colors for the reproduction of blue and red, i.e., magenta and cyan for blue, and magenta and yellow for red, so that the system has the problem of wasting the ink film and failing to ensure color registration.
The system further requires a prolonged period of time when making a single print since the transfer paper must then be reciprocatingly moved three times.
The use of the electrophotographic system for color printing similarly involves the problem of a failure in color registration and a prolonged printing time because the process for developing an electrostatic latent image with toner and transferring the toner image to copy paper must be repeated for each of different colors.
Further with the method employed for the conventional electronic print board, the separate items of image data obtained by the reading means for different color components are stored in different memories, and the printing means is initiated into operation for producing a color image based on the image data stored in the memories, after the image data for one page has been read. The method therefore requires a further prolonged period of time from the start of reading operation until the completion of printing operation. On the other hand, a color image forming apparatus has been proposed which is adapted to scan the original image every time the image is be printed in one of the component colors without using any memory, but when the apparatus is designed to print, for example, in the three colors of cyan, magenta and yellow, the original must be scanned three times. This entails the problem of producing a louder noise and causing early fatigue to the scanning means.